1. Field of the Invention
The present invention relates to a liquid-crystal (LC) orientating film, a method of manufacturing the film, and a LC element having the film.
2. Description of the Related Art
LC displays are small flat panel displays widely incorporated in desk-top calculators, watches, and similar small devices Recently, they have put to use in automobiles and personal computers. Further, they are now used as small-sized TV receivers, for displaying moving pictures.
These LC displays are almost identical in the structure of the LC cells they have. Each LC cell comprises a pair of substrates opposing each other, and a mass of liquid crystal filled in the gap between the substrates. The substrates are spaced apart for a predetermined distance by means of spacers, and are sealed together at their edges by means of sealing agent. Electrodes and an LC orientating film are formed on that surface of either substrate which faces the other substrate.
The LC orientating film is designed to orientate LC molecules in one direction. Two types of LC orientating films are available. The first type, which is more popular, orientates LC molecules parallel to the substrate. The second type, orientates LD molecules perpendicular to the substrate.
The LC orientating film is manufactured by either of the following methods:
(1) Rubbing method, wherein a polymer film such as a polyimide film or a polyvinyl alcohol film is formed on the surface of a substrate, and is rubbed with cloth such as velvet, thereby imparting LC-orientating ability to the polymer film. PA1 (2) Oblique vapor-deposition method, wherein vapor of a metal oxide such as SiO is applied in a line inclined at a predetermined angle to the substrate, thereby forming a metal oxide film on the surface of the substrate.
The rubbing method is employed in most cases, since it involves a simple process of rubbing the polymer film with cloth, and can produce many LC orientating films within a short time. This method, however, is not suitable for manufacturing large, high-precision LC displays for the following two reasons. First, as the film is rubbed with cloth, a great amount of static electricity is generated in the film, which damages thin-film transistors or cause dust to stick onto the substrate. Second, since the cloth contacts the substrate in most cases, the film is contaminated.
The oblique vapor-deposition method is rarely employed in practice for the following three reasons. First, it takes a long time to perform this method. Second, the LC molecules will have too large a pre-tilt angle. Third, the film formed by this method has but a poor LC orientating ability.